Metal spar for aircraft



H. N. WYLIE.

METAL SPAR FOR AIRCRAFT.

AFPLICATlON FILED AUG.22, 1919.

1,407,242. Pateilted Feb. 21, 1922.

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HAMILTON NEIL WYLIE, OF EDINBURGH, SOOTLAND, ASSIGNOB TO ARMSTRONG SIDDELEY MOTORS LIMITED, OF PARKSIDE, COVENTRY, ENGLAND.

METAL SPAR FOR AIRCRAFT.

Application filed August 22, 1919. Serial No. 319,245.

To all. whom it may concern Be it known that I, HAMILTON NEIL WYLIE, major in the Royal Air Force, a subject of the King of GreatBritain, residing at 19 Comiston Drive, Edinburgh, Scotland, have invented certain new and useful Improvements in Metal Spars for Aircraft, of whichthe following is a specification.

This invention relates to aeroplane spars and other members which are formed of thin metal, and more particularly to such members which are of girder form consistlng of two oppositely disposed booms connected by webs.

The invention consists essentially in adapt ing the thin metal, both of the booms and of the webs, to withstand longitudinal compression and shear stresses by curving it about longitudinal axes, so that its cross section is a series of sinuous curves. Each bay of the sinuous curve is curved to a suflicient degree to enable the metal to develop the necessary stresses. 7

In the accompanying drawings Figs. 1, 2, 3, 4 find 5 show in cross section examples of meta aeroplane spars constructed according to my invention, and Fig. 6 shows a detailed construction.

A preferred form of cross section is shown in Flg. 1 where the booms A consist of corrugated metallic strips of which the curvature of corrugation is not such as will cause the strip to fracture while being formed; and is still such as will enable the booms to develop high compression stress without local buckling. It has been found that for a compression stress of 100 tons per: square inch in steel members, the radius of curvature must not exceed times the thickness of the metal in a perfectly formed section, while in asection that is dented or irregular a smaller radius is necessary. For ordinary work a radius of curvature not exceeding 30 times the thickness is generally preferred.

The fittings necessary for transmitting loads to the spar will be adapted to distribute the loads properly over the webs and flanges, and to maintain the webs in their proper form where the loads are applied but such fittings do not form part of my present invention.

The edges of the Web B and the booms A are flanged so as to lie together and be connected by riveting, by electric welding or other suitable means. The extreme edges Specification of Letters Patent.

Patented Feb. 21, m2.

of the web are rolled to .a relatively small radius so as to form channels C, which receive the edges of the boom and hold them' in positlon during assembly. This formation of the small radius also stiifens the projecting flanges F, F, and prevents them from fail- 111 by cr nklmg under compressing stress. The sheets forming the'web B are also formed into longitudinal corrugations to enable them to withstand compression and shear. These corrugations have preferably a sharper curvature near to the booms where the compression stress may be greater than near to the centre. The central corrugations 1n the two sheets forming the web brin them into contact along the centre line and they are'directly connected together by, riveting. This connection greatly stiffens the sectlon against change of form.

The spar illustrated in Figure 2 is similar to that described in connection with Figure 1, except that the booms A have additional corrugations G and that the edges of the booms are rolled so as to embrace the flanged edges of the websas at F. Each of the sheets forming the web B, moreover, comprises two strips and all four-web straps are connected The spar illustrated in Figure 4 is similar to that described in connection with Figure 5, except that each part A, and adjacent parts B, are made from a single strip. This eliminates the flanges F, F, shown in Figure 1, with the result that thelines of connection of the booms to the web D are relatively close to the centre of the spar and are therefore relatively lightly stressed by forces tending to bend the spar.

Given a sufiiciently hard steel, a compression stress of tons per square inch can be developed in this section provided the circumference of each flange does not substantially exceed 200 times the thickness of the metal and that the radius of curvature of no outer part exceeds about thirty times th thickness of the metal.

In Figure 6 the flanged edge F of the web B is shown extended and bent over so as to embrace the curved edge F of the boom A.

When extreme lig itness is necessary the members hereinbefore described may have less thickness than foilows from the ratios given above as necessary to develop 106 tons per square inch in hard steei.

When the members are thus made in extremely thin metal, the extreme thinness may cause failure to occur before the metal is stressed to its elastic limit. The strength of such thin members when other things are equal has been-found to be substantially proportional to the elastic constant of the metal used.

The longitudinal corrugations of the Webs as Well as the flanges of the member is im v portant as it enables the metalto be reduced to one quarter of the least thickness which it would otherwise require to have to Withstand a given shear stress.

The forms of members described herein are suitable for other than aircraft structures.

What I claim as my invention and desire to secure by Letters Patent is 1. A metal girder comprising in combination two oppositely disposed booms of thin metal bent about longitudinal axes into sinuous curves, and a thin metal Web connecting said booms and bent about longitudinal axes into sinuous cu ves.

2. A metal girder comp: sing in combinaion two oppositely disposed booms of thin metal bent about longitudinal axes into sinuous curves, and a thin metal web connecting said boomscomposeu of a plurality of separate sheets bent about longitudinal axes into sinuous curves.

3. A. metal girder comprising in combination two oppositely disposed axioms of thin metal bent about longitudinal into sinuous curves, and a thin metal Web connecting said boomscomposed of a plurality of separate sheets bent about longitudinal axes imp sinuous curves, the edges of said Web and the edges of said booms being of similar curvature adapted for seating one agains the othen,

4t. A metal girder comprising in combination two oppositely disposed booms of thin metal bent about longitudinal axes into sinuous curves, and a thin metal web composed of a plurality of separate sheets bent about longitudinal axes into sinuous curves, the edges of the Web being extended and bent over so as to embrace the curved edges of the booms.

5. A metal girder comprising in combination two oppositely disposed booms of thin metal bent about longitudinal axes into sinuous curves, a thin metal web connecting said booms composed of two separate sheets bent about longitudinal axes into sinuous curves, the curves of one sheet in opposed relation to the curves of the second sheet. the central curve of the one sheet contacting with and secured to the central curve of the other sheet, the edges of the said sheets ionsing the web being secured to the edges oi: the upper and lower booms.

6. A metai girder comprising in comb n tion' two oppositely disposed vbooms of metal bent about longitudinal axes into sinuous curves, a thin metal web co eed of a plurality oi? separate sheets bent about longitudinal curves near the booms being sharp. the curves in the central portion of c the edges of the said sheets forming t being secured to the edges of the and lower booms.

In witness whereof l have hereunto .3 iv alien-es into sinuous curves the r 

